In a high-frequency package mounted with a semiconductor device that operates in a high-frequency band such as a microwave band or a millimeter-wave band, a surface-layer signal line or an inner-layer signal line formed in a multilayer dielectric substrate connects between an external terminal formed in the high-frequency package and an input and output terminal of the semiconductor device. Through these lines, a desired high-frequency signal is input and output, and also a direct current (DC) bias voltage and a control signal are input to and output from the semiconductor device.
In the high-frequency package, the semiconductor device that operates in the high-frequency band is shielded by a cover, a sealing, and a ground conductor surface. However, a high-frequency signal (unnecessary signal) as a spurious wave that leaks by conduction from the input and output terminal of the semiconductor device is emitted to the outside via a signal line for inputting and outputting a DC bias voltage and a control signal. Therefore, in a high-frequency package of this kind, it is very difficult to satisfy the electromagnetic interference (EMI) standards of various radio laws.
The entire machine module including such a high-frequency package may be covered with a metal cover. However, this requires an expensive casing and the like. Therefore, to minimize the cost, the EMI standards should desirably be satisfied in the high-frequency package.
Patent Document 1 discloses a conventional technology for absorbing an unnecessary high-frequency signal in a circuit board with a high-frequency component mounting part, a high-frequency transmission line connected to a high-frequency terminal of a high-frequency component, and a power supply circuit connected to a power supply terminal of the high-frequency component formed on the surface of a dielectric substrate. In the conventional technology, a power supply line and a via-hole conductor in the power supply circuit are formed with a high-permeability low-resistor having a relative magnetic permeability equal to or larger than 80, an electric resistivity equal to or less than 1.0 (μΩm), and including at least one of Fe, Co, and Ni.
Patent Document 1: Japanese Patent Application Laid-open No. 2004-39739